You may have read about my Kawai K1m in the development blog. Unfortunately, it is slightly broken and I thought, as there are so many people around still loving these old machines, that some of you could give a hint to repair it.
The issue is that the envelope attacks behave incorrectly. Short attack values are fine, but larger values cause the machine to end in complete silence.
With attack values larger than 36, the attack never finishes, decay is never reached and the sound is audible forever, no matter what the decay/sustain/release values are.
If the attack is even longer, starting with value of 50, the volume starts to decrease. The attack gets stuck so early that the voice keeps being very quiet. With a value of 69, the sound is not audible anymore at all. Below is a picture that shows attack values up to 69, where the voice becomes completely silent.
Anyone knows what is wrong? What I already tried:
- I added fresh solder to most ICs, including the CPU, the WaveROM (you might know) and the RAM chips
- I measured the connections between the three tone generators and between tone generators and CPU & Wave ROM, they’re all fine
- I upgraded the K1m firmware, I ordered a new chip with version 1.5, previously it had 1.3, no change
- I contacted Kawai and asked for help, unfortunately they have no idea
- I turned it off and on again 😎
My current assumption is that one of the Tone Generator chips is faulty and needs replacement. If there is anyone with another idea, that would be absolutely fantastic! 👍
Anyone with ideas? Thanks a lot in advance!